Method for producing highly pure aluminum primary base metal

ABSTRACT

The present invention provides a method of producing a highly pure aluminum primary base metal having a purity of at least 99.95 wt % (3N5), or a still higher purity close to the 4N that is a purity value of a secondary refined base metal.Alumina, the Si component of which is decreased by acid cleaning, is placed in a Hall-Heroult electrolysis cell as a main raw material. An aqueous solution of sulfuric acid, an aqueous solution of sulfuric acid plus hydrofluoric acid, or the like is used for acid cleaning. In order to remove Si, an acidic aqueous solution heated to at least 40° C. is preferred. Use of deashed coke and/or pitch as a carbon material for anode in addition to the use of acid-cleaned alumina produces a highly pure aluminum primary base metal in which the Si and Fe components are further decreased.

TECHNICAL FIELD

The present invention relates to a method of producing an aluminumprimary base metal by electrolysis.

BACKGROUND ART

An aluminum base metal has been principally produced by Hall-Heroultelectrolysis. In Hall-Heroult electrolysis, alumina, that is aluminumoxide, and a carbon material for an anode are used as a main rawmaterial and an additive raw material, respectively.

Alumina is usually prepared from alumina-containing ore such as bauxiteby alkali extracting and calcining, and is supplied as powder to anelectrolysis cell. Alumina prepared in such a manner as explained aboveusually has a purity of about 98.5 wt %. The alumina has a moisturecontent and contains from several tens to several hundred of ppm each ofmetal oxides such as Fe, Si, Ga, V and Ti as shown in Table 1.

The carbon material for anode used as an additive raw material isprepared by mixing calcined coke and a binder in a predeterminedproportion and compacting the mixture into briquettes, and is suppliedto the top of the anode of an electrolysis cell. Moreover, thesematerials are sometimes compacted and fired in advance, and set in theelectrolysis cell. The carbon material for anode is consumed as theelectrolytic reduction of alumina (aluminum oxide) proceeds. The carbonmaterial used in the anode is a mixture of coke and pitch, and containsabout several hundred ppm each of oxides such as Fe, Si, V and Ti. Thisis because the ordinary purity of coke and pitch is as shown in Table 2.

TABLE 1 Contents of Impurity Elements Usually Contained in AluminaImpurity elements Content (ppm) Si 60-350 Fe 30-200 Cu 0-20 Ni 0-20 Ti0-60 Mn 0-30 V 0-30 Sn 0-30 Zn 0-60 Cr 0-30 Pb 0-30 Zr 0-15 Bi 0-10 Ga30-200

TABLE 2 Contents (ppm) of Impurity Elements Usually Contained in Cokeand Pitch Impurity elements Content in coke Content in pitch Si 100-300 70-210 Fe 20-150  14-110 Cu 0-20  0-14 Ni 0-100 0-70 Ti 1-100 1-70 Mn1-100 1-70 V 1-300  1-210 Sn 1-200  1-140 Zn 0-60  0-42 Cr 0-100 0-70 Pb0-50  0-35 Zr 0-50  0-35 Bi 0-10  0-7  Ga 0-20  0-14

Although the impurities contained in the alumina (main raw material) andthe carbon material for anode (additive raw material) are partly removedduring electrolysis, a significant amount is transferred to the product.As a result, the maximum purity of primary aluminum obtained byelectrolysis is 99.9 wt % (hereinafter referred to as 3N).

In the present specification, the purity of an aluminum base metal isdefined as a value obtained by subtracting the total content of the mainimpurity elements of Si, Fe, Cu, Ni, Ti, Mn, V, Sn, Zn, Cr, Pb, Zr, Biand Ga (14 elements) from 100 wt %.

On the other hand, in the field of electrolytic capacitors, magneticdiscs and the like where demand for highly pure aluminum has beengrowing in recent years, aluminum having a purity of about 3N cannotmeet the requirements for the properties of the capacitors, discs andthe like; demand for highly pure aluminum having a purity of at least99.95% (hereinafter referred to as 3N5) has been growing.

In order to surely meet the quality requirements explained above, thepurity of the aluminum base metal has heretofore been improved by asecondary refining step, by the three layer electrolysis and by thesegregation process. However, since the improvement requires a secondaryrefining step, the production cost rises, and the production efficiencydeclines.

DISCLOSURE OF INVENTION

An object of the present invention is to solve the problems related tothe conventional technologies described above, and to provide a methodof stably producing an aluminum primary base metal having a purity of atleast 99.95 wt % (3N5) by electrolysis.

In order to achieve the object described above, a first invention of thepresent invention provides a method of producing a highly pure aluminumprimary base metal, the method comprising placing, as a main rawmaterial, alumina, the Si component of which has been decreased by acidcleaning, in a Hall-Heroult electrolysis cell.

In the acid cleaning, an aqueous solution of sulfuric acid, hydrofluoricacid, or sulfuric acid plus hydrofluoric acid etc. is used, and anacidic aqueous solution heated at temperature of at least 40° C. isparticularly preferred from the standpoint of removing Si.

According to a second invention of the present invention, the objectexplained above is also achieved by a method, of producing an aluminumprimary base metal, which comprises preparing an electrolysis anode byusing deashed coke and/or pitch as a carbon material for the anode, andcharging the electrolysis anode into a Hall-Heroult electrolysis cell asan additive raw material.

As a result of using the production methods of the first and the secondinvention in combination, a highly pure aluminum in which the impuritycontents including the Si and the Fe content are further decreased canbe produced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the influence of the time of acid-cleaningalumina, on a residual Si content in acid cleaning, with an aqueoussolution containing 10% of sulfuric acid.

FIG. 2 is a graph showing the influence of the time for acid-cleaningalumina, on a residual Si content in acid cleaning, with various aqueoussolutions.

BEST MODE FOR CARRYING OUT THE INVENTION

Alumina produced by a conventional apparatus is basically used as themain raw material alumina. The alumina is produced by a process designedto decrease the inclusion amounts of Fe and Si components derived fromthe production apparatus.

Specifically, inclusion of the Fe and the Si component is suppressed byprocedures including the following ones: aluminum hydroxide crystalsprecipitated after extracting bauxite with sodium hydroxide are moreadequately cleaned in the step of separation filtering; moreover, in thestep of calcining the filtered aluminum hydroxide crystals, thecalcination temperature is lowered, and a calcination furnace lined withhigh alumina refractories having a low Si content is used.

The alumina thus produced is acid-cleaned before charging it into anelectrolysis cell.

The present inventors have found that most of the impurities in aluminasegregate in the surface layer of the alumina particles, and thatremoval of the surface layer portions thereof by acid cleaning greatlydecreases the impurity content. Typically, 70% of the Si content ofalumina segregate in the surface layer (volume ratio of 5 to 10%) of thealumina particles.

Acid cleaning dissolves and elutes SiO₂, Fe₂O₃ and trace impurityelements such as Zn contained in alumina and further transfers ultrafineparticles to the solution system. Since impurities that exert adverseeffects on the electrostatic capacity and the resistance to pressure ofelectrolytic capacitors when the aluminum is used therefor, and thatcause troubles such as blisters when the aluminum is used for magneticdiscs are removed by acid cleaning, the resultant alumina becomes a rawmaterial for producing high quality aluminum primary base metal.

The alumina is usually dried after acid cleaning. Removal of impuritiesin the alumina proceeds to some extent even by water cleaning; however,the removal effect is small in comparison with acid cleaning.

A mixture of aggregate coke and binder pitch is used as a carbonmaterial for anode of an additive raw material. Although examples of araw material for aggregate coke include pitch coke obtained by calciningcoal tar pitch, and oil coke obtained by calcining crude oil, pitch cokeprepared from relatively highly pure coal tar is preferred.

The aggregate coke is prepared by deashing raw material coal tar andcalcining the deashed tar. Although elements included in the rawmaterial coal tar differ depending on the place of production of thecoal, the coal tar usually contains 0.01 to 1% of an ash componentmainly composed of SiO₂ and Fe₂O₃. Since these elements show the samebehavior in the metal as in the alumina, the contents of these elementsare desirably low when the aluminum is used for electrolytic capacitors,magnetic discs or the like. Accordingly, raw material coal tar istreated with an organic solvent, and the ash component of the coal taris separated by redistillation to give highly pure coal tar. Theresultant coal tar is then calcined, and the calcined coal tar is usedas carbon aggregates for anode.

Prior to calcination of the coal tar, it is preferred to make thecrystalline state during calcination equiaxed grains (granular crystals)by adding seeds for crystal formation and crystal growth of the rawmaterial tar. The seeds are added for the following reasons. Thecrystallization direction of the coke obtained by calcining the rawmaterial tar without adding the seeds become nonuniform, and needle-likecrystals grow. The needle-like crystals show poor chemical reactivitywhen electrolysis is conducted using a carbon anode prepared by mixingaggregate coke and binder pitch. As a result, the proportion of the cokethat does not contribute to an effective electrochemical reaction, andthat is consumed mechanically or by mere combustion increases.

Deashed highly pure tar pitch is used as a binder for the anode of theadditive raw material. The tar pitch can also be used without furtherprocessing; however, carbon black, mesophase carbon or crystallizedcarbon that is once pulverized is preferably added to the tar pitch toimprove the binder properties, and the resultant tar pitch is preferablyused.

The alumina (main raw material) and the carbon material for anode(additive raw material) thus prepared are charged into an electrolysiscell with fluorine compound-containing cryolite used as an electrolyticbath, and subjected to an electrolytic reaction. The charged alumina isdissolved in molten cryolite, and an electrolytic reduction reactionproceeds with the carbon electrode material being contacted with themolten cryolite bath. Metallic impurities such as Fe and Si contained inthe main and additive raw materials are also dissolved into the moltencryolite to cause a reduction reaction, and part of them are vaporizedas fluorides and discharged together with an exhaust gas.

The discharge proportion of the impurities increases in accordance witha reduction potential during the electrolysis. The discharge proportionof Fe is 30 wt %, and that of Ga is as much as 50 to 60 wt %. An exhaustgas containing impurities such as Fe and Ga as fluorine compounds istreated by wet recovery in which the fluorine component is absorbed intoaqueous alkali. In the wet recovery, sodium hydroxide is commonly usedfor aqueous alkali for absorbing the exhaust gas, and the fluorinecomponent is fixed as sodium fluoride (NaF). The NaF is treated withsodium aluminate or aluminum sulfate to regenerate cryolite. Althoughthe regenerated cryolite can be recycled as an electrolytic bath, thecryolite is unsuitable for the production of highly pure aluminumbecause it contains impurities. On the other hand, the dry scrubbingmethod in which a discharged fluoride is absorbed into the raw materialalumina is not preferred because the method results in recovering evendischarged impurities.

The aluminum primary base metal obtained by electrolysis using thealumina (main raw material) and/or the carbon material (additive rawmaterial) for anode thus prepared is a highly pure base metal having aquality comparable to or practically identical to the conventionalsecondary refined base metal.

EXAMPLES Example 1

Using a production apparatus that suppressed the inclusion of Fe, Si andthe like, a calcined alumina Al having a Si content of 40 to 60 ppm wasproduced. The calcined alumina was acid-cleaned under variousconditions, and the residual Si content of the calcined alumina wasmeasured. The following acid cleaning conditions were selected. The acidcleaning was conducted at temperatures at two levels: 60° C. and 80° C.The acid cleaning was conducted in solutions at 3 levels: an aqueoussolution containing 10% of sulfuric acid; an aqueous solution containing0.5% of hydrofluoric acid; and an aqueous solution containing 10% ofsulfuric acid and 0.5% of hydrofluoric acid.

When the relationship between a measured value of a residual Si contentand an acid-cleaning time was examined, it was found that the residualSi content fell in accordance with the lapse of the acid-cleaning time.As shown in FIG. 1, in acid cleaning with an aqueous solution containing10% of sulfuric acid (80° C.), alumina (hereinafter referred to ashighly pure alumina S) having a Si content that was lowered to notgreater than half of that of the alumina prior to the acid cleaning wasobtained after acid cleaning for 40 minutes. As shown in FIG. 2, in acidcleaning with an aqueous solution containing 0.5% of hydrofluoric acid,or 10% of sulfuric acid plus 0.5% of hydrofluoric acid (60°C., 80° C.),alumina (hereinafter referred to as highly pure alumina SF) having a Sicontent that was lowered to not greater than ¼ of that of the aluminaprior to the acid cleaning was obtained after acid cleaning for 20 or 30minutes. However, a decrease in the Fe content caused by acid cleaningwas very slight.

The recovery of alumina subsequent to cleaning was 99% whennon-acid-treated alumina was treated for 40 minutes with an aqueoussolution containing 10% of sulfuric acid (60° C., 80° C.), and 94% whennon-acid-treated alumina was treated for 20 minutes with an aqueoussolution containing 0.5% of hydrofluoric acid, or 10% of sulfuric acidplus 0.5% of hydrofluoric acid (60° C., 80° C.).

Highly pure alumina S was supplied to an electrolysis cell in which aconventional anode material was used and, when the molten aluminum inprocess, stored within the cell, was completely replaced, the contentsof the impurities were measured. As a result, the content of theimpurity Si was lowered from the level of 200 ppm when charging aluminathat was not acid-cleaned to the level of 140 ppm or less (a decrementof 60 ppm).

Table 3 shows the contents of the main impurities described above andthe purity of the aluminum base metal. In addition, Table 3 also shows,for comparison, conventional field-proven values obtained by procedureswherein a conventional anode material that was not deashed was used,alumina was produced by a conventional alumina production apparatus, andthe alumina was not cleaned.

TABLE 3 Contents (ppm) of Impurities and Purities (wt %) of AluminumBase Metals Example 1 Conventional Example Alumina A Company, alumina SA Company, commercial Coke Conventional Conventional Pitch ConventionalConventional Impurity Elements Si 100-140 180-200 Fe 135-170 200-250 Cu1-5 10-20 Ni 1 1 Ti 20-30 20-30 Mn 5 5-7 V 1-2 2-3 Sn 5 5 Zn 25-35 25-35Cr 2 1 Pb 3-5 3-5 Zr 5 5 Bi 1 1 Ga  70-100  70-100 Purity of base metal99.963-99.949 99.947-99.934 Note: Table 3 shows analytical resultsobtained by sampling once a day for a test period (3 months). Each ofthe data shown in a range is a maximum and a minimum value during thetest period (3 months). Each of the data shown as a single numericalvalue is a value that did not vary within the significant digit ordigits.

As shown in Table 3, even the upper limit of the field-proven values isslightly smaller than the purity 99.95 wt %, and the lower limit thereofis significantly smaller than the purity 99.95 wt % in ConventionalExample. In contrast to the results explained above, in Example 1 inwhich alumina was cleaned according to the present invention, all thefield-proven values including the lower limit substantially attained thepurity 99.95 wt %.

As explained above, the present invention can stably ensure the purity99.95 wt %.

Example 2

Carbon black fine powder was added to highly pure coal tar obtained bydissolving coal tar pitch in an organic solvent, and redistilling thesolution to effect deashing. The mixture was calcined at an averagecalcination temperature of 1,100° C. to give aggregate coke forelectrolysis anode. Moreover, electrode-impregnating pitch prepared bydeashing and adding carbon black in the same manner as explained abovewas purchased as binder pitch for anode. The Fe content of the purchasedhighly pure coke and that of the highly pure pitch were 2 ppm and 5 ppm,respectively; the Si content thereof and that of the highly pure pitchwere 5 ppm and 5 ppm, respectively; the Cu content thereof and that ofthe highly pure pitch were less than 1 ppm and less than 1 ppm,respectively. The total content of the other impurity elements excludingAl of the purchased coke and that of the highly pure pitch were eachless than 3 ppm.

Highly pure self-firing anode briquettes were produced using theaggregate coke and electrode-impregnating pitch. The briquettes werecharged into the top of the anode of an electrolysis cell to be made inprocess. Alumina produced in the step designed to decrease the inclusionamounts of Fe and Si, was supplied when the anode reached the reactionsurface, i.e., in about 3 months; moreover, when the molten aluminum inprocess stored within the cell was completely replaced, the contents ofthe impurities were measured. As a result, it was found that the contentof impurity Fe was lowered from the level of 250 ppm to 90 ppm or less,and that the content of impurity Si was lowered from the level of 200ppm to 120 ppm or less.

Table 4 shows the contents of the main impurities and the purity of thealuminum base metal described above. In addition, Table 4 also shows,for comparison, conventional field-proven values obtained by a procedurewherein a conventional anode material that was not deashed was used,alumina was produced by a conventional alumina production apparatus, andthe alumina was not cleaned.

TABLE 4 Contents (ppm) of Impurities and Purities (wt %) of AluminumBase Metals Conventional Example 2 Example Alumina A Company, A Company,commercial (*) commercial Coke Deashed Conventional Pitch DeashedConventional Impurity elements Si 100-120 180-200 Fe 65-90 200-250 Cu1-5 10-20 Ni 1> 1 Ti 20-30 20-30 Mn 5 5-7 V 1 2-3 Sn 5 5 Zn  5-15 25-35Cr 2 1 Pb 1> 3-5 Zr 5 5 Bi 1 1 Ga 70-90  70-100 Purity of base metal99.972-99.963 99.947-99.934 Note: Table 4 shows analytical resultsobtained by sampling once a day for a test period (3 months). Each ofthe data shown in a range is a maximum and a minimum value during thetest period (3 months). Each of the data shown as a single numericalvalue is a value that did not vary within the significant digit ordigits. (*) A step in which the inclusion amounts of the Fe and the Sicomponent were decreased was performed.

As shown in Table 4, the field-proven values did not attain the purity3N5 in Conventional Example. In contrast to the results explained above,in Example 2 in which coke and pitch (anode materials) were deashedaccording to the present invention, all the field-proven valuesincluding the lower limit attained the purity 3N5.

As explained above, according to the present invention, a purity of atleast 99.95 wt % (3N5) can be stably ensured for the aluminum basemetal.

Concerning the effect of decreasing the amount of impurities by deashingthe anode materials in the present example, it should be particularlynoted that the Pb content was lowered from the conventional value of 3to 5 ppm to less than 1 ppm.

For example, when the aluminum base metal is worked to form a foil foran electrolytic capacitor, the foil must be heat-treated, whereby Pb isconcentrated on the foil surface. As a result, the foil surface portionsubsequent to the heat treatment has a Pb content that is from 10 to 100times as great as the average Pb content. The concentration of Pbtherefore exerts adverse effects on the capacitor characteristics. Nosuch adverse effects are produced after decreasing the Pb content in thepresent invention.

Example 3

The following aggregate coke for electrolysis anode was purchased andprepared. In the same manner as in Example 2, carbon black fine powderwas added to highly pure coal tar obtained by dissolving coal tar pitchin an organic solvent, and redistilling the solution to effect deashing.The mixture was calcined at an average calcination temperature of 1,100°C. to give aggregate coke for electrolysis anode. Conventional electrodepitch was purchased and prepared as binder pitch for anode. The purityof the purchased highly pure coke was the same as in Example 2. Thepurchased conventional electrode pitch had an Fe content of 37 ppm, a Sicontent of 171 ppm and a Cu content of less than 1 ppm.

Self-firing anode briquettes were produced using the aggregate coke andelectrode pitch. The briquettes were charged into the top of the anodeof an electrolysis cell to be made in process. Alumina produced in thestep that was designed to decrease the inclusion amount of the Fe andthe Si component was supplied at the stage where the anode reached thereaction surface in about 3 months; moreover, when the molten aluminumin process stored within the cell was completely replaced, the contentsof the impurities were measured. As a result, it was found that thecontent of impurity Fe was lowered from the level of 250 ppm to 150 ppm,and that the content of impurity Si was lowered from the level of 200ppm to 170 ppm.

Table 5 shows the contents of the main impurities and the purity of thealuminum base metal described above. In addition, Table 5 also shows forcomparison conventional field-proven values obtained by a procedurewherein a conventional anode material that was not deashed was used, andalumina was not cleaned.

TABLE 5 Contents (ppm) of Impurities and Purities (wt %) of AluminumBase Metals Conventional Example 3 Example Alumina A Company, A Company,commercial (*) commercial Coke Deashed Conventional Pitch ConventionalConventional Impurity elements Si 120-145 180-200 Fe 70-95 200-250 Cu1-5 10-20 Ni 1 1 Ti 20-30 20-30 Mn 5-6 5-7 V 1 2-3 Sn 5 5 Zn 20-30 25-35Cr 1 1 Pb 2 3-5 Zr 5 5 Bi 1 1 Ga 70-90  70-100 Purity of base metal99.967-99.958 99.947-99.934 Note: Table 5 shows analytical resultsobtained by sampling once a day for a test period (3 months). Each ofthe data shown in a range is a maximum and a minimum value during thetest period (3 months). Each of the data shown as a single numericalvalue is a value that did not vary within the significant digit ordigits. (*) A step in which the inclusion amounts of the Fe and the Sicomponent were decreased was performed.

As shown in Table 5, even the upper limit of the field-proven values inConventional Example did not attain the purity 3N5. In contrast to theresults explained above, in Example 3 in which coke (anode material)alone was deashed, all the field-proven values including the lower limitattained the purity 3N5.

The effect of decreasing impurities by deashing coke alone in thepresent example is small in comparison with the example in which boththe coke and pitch were deashed. That is, it is more desirable to deashboth the coke and pitch than to deash the coke alone.

As explained above, according to the present invention, a purity of atleast 99.95 wt % (3N5) can be stably ensured for the aluminum basemetal.

Although the effect of decreasing Pb is more reduced in the presentexample than in Example 2, the content of Pb was lowered from theconventional value of 3 to 5 ppm to 2 ppm.

Example 4

The highly pure self-firing anode briquettes used in Example 2 werecharged into the top of the anode of an electrolysis cell to be made inprocess. When the anode reached the reaction surface, i.e., in about 2months, supply of highly pure alumina S was started.

When molten aluminum in process stored within the cell was completelyreplaced, the contents of the impurities were measured. It is seen fromthe measurement results in Table 3 that as a result of using highly purealumina S, deashed coke and deashed pitch, aluminum primary base metalseach having an Si content of 60 ppm or less, and an Fe content of 80 ppmor less were obtained.

Table 6 shows the contents of the main impurities and the purities ofthe aluminum base metals described above. In addition, Table 6 alsoshows for comparison conventional field-proven values obtained by aprocedure wherein a conventional anode material that was not deashed wasused, alumina was produced with a conventional alumina productionapparatus, and the alumina was not cleaned.

TABLE 6 Contents (ppm) of impurities and Purities (wt %) of AluminumBase Metals Conventional Example 4 Example Alumina A Company, B Company,A Company, alumina S alumina S commercial Coke Deashed DeashedConventional Pitch Deashed Deashed Conventional Impurity elements Si40-60 40-60 180-200 Fe 50-80 45-70 200-250 Cu 1-5 1-5 10-20 Ni 1> 1> 1Ti 20-30 10-20 20-30 Mn 5 2 5-7 V 1 1 2-3 Sn 5 1 5 Zn  5-15  3-10 25-35Cr 2 1 1 Pb 1> 1> 3-5 Zr 5 2 5 Bi 1 1> 1 Ga 70-90 30-40  70-100 Purityof base metal 99.980-99.970 99.986-99.979 99.947-99.934 Note: Table 6shows analytical results obtained by sampling once a day for a testperiod (3 months). Each of the data shown in a range is a maximum and aminimum value during the test period (3 months). Each of the data shownas a single numerical value is a value that did not vary within thesignificant digit or digits.

As shown in Table 6, the field-proven values in Conventional Example didnot attain the purity 3N5.

In contrast to the results explained above, in Example 4 in which theanode materials were deashed and/or the alumina was cleaned, all thefield-proven values including the lower limit exceeded the purity 3N5,and attained the purity of at least 99.97 wt % which is close to 4N.

As explained above, the present invention can stably ensure the purityof at least 99.95 wt % (3N5).

INDUSTRIAL APPLICABILITY

explained above, in the present invention, alumina the Si component ofwhich is decreased by acid cleaning is used as a main raw material, andelectrolysis is conducted to give a highly pure aluminum primary basemetal having a purity of at least 99.95 wt % (3N5). Moreover, use of adeashed carbon material for anode in combination with the alumina givesan aluminum primary base metal meeting the requirements for theproperties of electrolytic capacitors, discs and the like and having apurity close to the purity 4N of an aluminum secondary refined basemetal.

What is claimed is:
 1. A method of producing a highly pure aluminumprimary base metal, comprising placing alumina, the Si content of whichhas been decreased by acid cleaning, in a Hall-Heroult electrolysis cellas a main raw material.
 2. The method according to claim 1, whereinalumina having been acid-cleaned with an aqueous solution of sulfuricacid and/or hydrofluoric acid is used.
 3. The method according to claim1, wherein deashed coke and/or pitch is used as a carbon material for ananode.
 4. A method of producing a highly pure aluminum primary basemetal, comprising preparing an electrolysis anode using deashed cokeand/or pitch as a carbon material for the anode, and charging theelectrolysis anode into a Hall-Heroult electrolysis cell as an additiveraw material; wherein the deashed coke is prepared by treating a rawmaterial coal tar with an organic solvent, deashing the treated coal tarby redistillation and calcining the deashed coal tar, and the deashedpitch is prepared by treating a raw material coal tar pitch with anorganic solvent and deashing the treated coal tar pitch byredistillation.